Range hood CFM (cubic feet per minute) is the amount of air a hood’s blower can move. Most homes need less than the biggest hoods offer: a 30 inch electric or induction cooktop against a wall is well served by about 250 CFM, while a high output gas range or an island cooktop needs more. Here are the two sizing rules, how ducting and makeup air change the answer, and which hoods we carry fit each case.
How many CFM range hood do I need?
There are two common rules, and you should use the one that matches your cooktop.
Electric and induction: size by width
The Home Ventilating Institute (HVI) recommends 100 CFM per linear foot of cooktop for a hood against a wall, with 40 CFM per foot as the minimum. For an island hood it recommends 150 CFM per linear foot (50 minimum), because there is no wall to help channel smoke. In its sizing table, HVI lists 250 CFM recommended for a 30 inch wall hood, 300 CFM for 36 inches and 400 CFM for 48 inches.
Gas: size by burner BTU
Gas burners put out more heat, so the common rule is based on total burner output. Broan-NuTone’s guidance is a minimum of 100 CFM per 10,000 BTU, so a stove with 50,000 BTU of total burner output calls for about 500 CFM (Broan-NuTone CFM guide). Add up the BTU ratings of every burner on your spec sheet, divide by 100, and use the higher of that number or the width rule. The EPA also recommends an exhaust fan vented to the outdoors over gas stoves, because unvented gas cooking is a source of nitrogen dioxide indoors (EPA: nitrogen dioxide and indoor air). If you are still choosing the cooktop itself, our induction vs gas cooktop guide covers that decision.
Range hood CFM quick chart
These are starting points from the rules above. The gas rows are our math using 100 CFM per 10,000 BTU; use your own cooktop’s total BTU.
| Setup | Rule | Starting CFM |
|---|---|---|
| 30 inch electric or induction, wall | HVI, 100 CFM per foot | 250 |
| 36 inch electric or induction, wall | HVI, 100 CFM per foot | 300 |
| 36 inch cooktop, island | HVI, 150 CFM per foot | 450 (our math: 3 ft x 150) |
| Gas range with 40,000 BTU total | 100 CFM per 10,000 BTU | 400 (our math) |
| Gas range with 50,000 BTU total | 100 CFM per 10,000 BTU | 500 (Broan example) |
Range hood size for 30 inch stove
Width matters as much as CFM. A hood should cover the full cooking surface, so a 30 inch stove gets at least a 30 inch hood. Height matters too. Empava’s install manuals give these clearances between the cooking surface and the bottom of the hood:
- 30RH05 wall mount and 36RH10 island: 24 to 33 inches.
- 30RH07 under cabinet: 26 to 30 inches, and the manual says 30 inches is needed over a gas stove.
Always follow the manual for your exact model and your cooktop maker’s clearance, whichever is stricter.
Duct size and duct runs
CFM ratings assume the air can actually leave. Every Empava ducted hood below lists a 6 inch round duct on Empava’s spec sheets. Broan-NuTone notes that the minimum duct allowed is 3 x 10 inches and that a longer duct run raises the CFM you need. Practical rules:
- Use the outlet size the manual lists; do not reduce it.
- Keep the run short. Empava’s manuals say to minimize duct length, and Broan-NuTone notes that longer ducts raise the CFM you need.
- Use metal duct. Empava’s manuals warn to use only metal ductwork to reduce fire risk.
- Vent to the outdoors. Empava’s manuals say not to connect the hood outlet to combustion gas ducts or to ventilation ducts for rooms with fuel-burning appliances.
Makeup air range hood 400 CFM rule
The International Residential Code (section M1503, “Makeup air required”) requires makeup air for kitchen exhaust systems capable of exhausting more than 400 CFM, with dampers that open automatically when the hood runs. As Green Building Advisor explains, the 2018 edition applies this where fuel-fired appliances are inside the home’s envelope (Green Building Advisor on makeup air). Local adoption varies, so ask your building department.
The practical effect: a 400 CFM hood stays at the threshold, while a 500 CFM or larger hood can trigger a makeup air system, which adds ductwork and cost. If the width rule says 250 to 300 CFM, buying 900 CFM only adds noise and possibly a makeup air bill.
Ducted vs ductless range hood
A ducted hood sends air outside. A ductless (recirculating) hood pulls air through grease filters and charcoal filters, then returns it to the kitchen. Ductless hoods trap grease and some odor, but they do not remove heat, moisture or combustion gases from the house, which is why ducted is the better choice over gas.
Ductless makes sense where you cannot run a duct. Budget for charcoal filter replacements: for the Empava 30RH15F we carry the replacement charcoal filter at $13.29. CIARRA convertible hoods on our iio Kitchen brand page list CFM and sones but not duct size, so call us to confirm before you plan a ducted install.
Noise: dB and sones
Empava lists noise below 65 dB for its 500 CFM under cabinet hoods and 66 dB for the 300 CFM ductless model. Some makers rate noise in sones instead; a lower sone number is quieter. HVI notes that hoods with multiple speeds allow quiet, low level ventilation for light cooking. A correctly sized hood is usually the quieter choice.
Empava range hoods by CFM
Specs below are from Empava’s own product pages. Our prices match Empava’s direct prices as of October 2026, but Empava ships free in the contiguous US, while we charge $200 shipping on orders under $999. For a single hood, buying direct from Empava is cheaper delivered. Our prices make sense when the hood is part of a larger order that qualifies for our free freight at $999 or more.
| Model | Type | Width | CFM | Duct | Our price |
|---|---|---|---|---|---|
| Empava 30RH15F | Ductless under cabinet | 30 in | 300 | None (recirculating) | $177.59 |
| Empava 30RH05 | Wall mount, ducted | 30 in | 400 | 6 in round | $214.79 |
| Empava 30RH07 | Under cabinet, ducted | 30 in | 400 | 6 in round | $235.69 |
| Empava 30RH11 | Under cabinet, ducted | 30 in | 500 | 6 in round | $339.69 |
| Empava 36RH12 | Under cabinet, ducted | 36 in | 500 | 6 in round | $359.99 |
| Empava 36RH10 | Island, ducted | 36 in | 400 | 6 in round | $495.39 |
How to read this: a 30 inch electric or induction cooktop on a wall is covered by the 400 CFM 30RH05 or 30RH07 without crossing the makeup air threshold. A 30 inch gas range with around 50,000 BTU total points to the 500 CFM 30RH11, so check your local makeup air rule first. For a 36 inch island, HVI’s rule gives 450 CFM (our math), slightly above the 400 CFM 36RH10, so it fits best over a lower output or electric cooktop. See every model on our Empava brand page. Restaurant hoods are a separate category; our commercial kitchen equipment guide covers that.
Frequently asked questions
How many CFM range hood do I need for a 30 inch gas stove?
Add up the burner BTU ratings and use 100 CFM per 10,000 BTU. A 30 inch range with 40,000 BTU total needs about 400 CFM by our math; one with 50,000 BTU needs about 500.
Do I need makeup air for a 500 CFM range hood?
Possibly. The IRC requires makeup air for kitchen exhaust capable of more than 400 CFM, and the 2018 edition ties this to fuel-fired appliances inside the home. Your local code decides, so check with your building department before buying.
Is a ductless range hood as good as a ducted one?
No. A ductless hood filters grease and some odor but returns heat and moisture to the room. Choose ducted whenever you can vent outside, especially over gas.
Does CFM change with longer ducts?
Yes. Broan-NuTone notes that as duct length increases, so does the CFM you need. Keep runs short and at the full outlet size the manual lists. Questions about a specific hood? Call us at 866-777-2590, Monday to Friday, 9AM to 6PM PST. Our return and refund policy is here.
